The invention discloses an immersed tube construction technique. The invention provides a portable waterstop protection device for an immersed tube tunnel which comprises a grooved steel plate; the width of the groove of the grooved steel plate is greater than the size of the splicing joint of every two adjacent immersed tube sections; the waterstop protection device further comprises positioningribs which fix the grooved steel plate on the immersed tube sections; the positioning ribs are made of a flexible material, so that the two sides of the grooved plate are separately arranged on the immersed tube sections on two sides of the splicing joint. The protection device is simple in assembly and disassembly; compared with a protection structure of laying steel plates, the portable waterstop protection device has the advantages that construction difficulty is reduced, and the construction period is shortened; besides, due to the reliable grooved steel plate and the fixing mode, a hermetic environment is formed by a waterstop; the waterstop is effectively protected; and the grooved steel plate can be repeatedly utilized, so that materials are saved, and cost is reduced.